Conventionally, there have been employed disc players for reproducing information recorded on read-only type optical discs, and for recording information to recording type optical discs and reproducing information recorded thereon. Such a disc player includes a disc tray onto which a plurality of optical discs are placed for loading, and a tray shift mechanism for shifting or moving the disc tray internally to and externally from the main body of the disc player.
The disc tray has the main surface which is provided with a plurality of disc placement recesses onto which a plurality of optical discs are to be placed. The disc tray is so arranged in the disc player as to be able to shift between a setting/taking-out position where an optical disc is set/taken out onto/from the disc tray and a playback position where information recorded on an optical disc is reproduced.
The tray shift mechanism includes a planetary gear mechanism for shifting the disc tray, and a drive mechanism for driving or rotating the planetary gear mechanism.
As shown in FIG. 1, a conventional planetary gear mechanism 200 of the tray shift mechanism includes a sun gear 201 which is driven or rotated by the drive mechanism, a planet gear 202 which is engaged with the sun gear 201, and an inner-tooth-rack 203 substantially of a U shape which has teeth provided on the inner side thereof and is engaged with the planet gear 202.
The sun gear 201 has a pivot shaft 205 at the center thereof, and is caused to rotate along with the pivot shaft 205 when the pivot shaft 205 is driven or rotated by a motor, not shown, of the drive mechanism.
The planet gear 202 has a pivot shaft 206 at the center thereof, and has a large-tooth-portion 207 which is engaged with the sun gear 201, and a small-tooth-portion 208 which has a pitch circle smaller than that of the large-tooth-portion 207 and is engaged with the inner-tooth-rack 203.
The inner-tooth-rack 203 is unitedly formed at around the rear end of the disc tray, and is engaged with the small-tooth-portion 208 of the planet gear 202.
The disc tray is provided with a guide ditch 211 for guiding the planet gear 202 inside and along the inner-tooth-rack 203, in which the pivot shaft 206 is movably arranged. That is, the revolution operation of the planet gear 202 is assisted by the guide ditch 211 with the small-tooth-portion 208 thereof engaged with the inner-tooth-rack 203.
In thus configured planetary gear mechanism 200, when the sun gear 201 is caused to rotate by the drive mechanism, not shown, the large-tooth-portion 207 of the planet gear 202 is rotated. When the large-tooth-portion 207 of the planet gear 202 is rotated, the small-tooth-portion 208 of the planet gear 202 is rotated along the inner-tooth-rack 203, while concurrently the planet gear 202 is caused to revolve around the sun gear 201 with the pivot shaft 205 being its revolution center.
Thus, in the planetary gear mechanism 200, when the small-tooth-portion 208 of the planet gear 202 is rotated, the inner-tooth-rack 203 is shifted, which causes the disc tray having the inner-tooth-rack 203 to shift between the setting/taking-out position and the playback position.
Generally, in a gear mechanism, in case of using gears made of resin, the distance between the centers of a pair of gears which are engaged with each other is so designed as to be slightly larger than the sum of radiuses of pitch circles of the respective gears. This is to cope with or prevent interference such as clog between respective gears due to error of negative value which may arise between centers of formed gears or expansion of gears with heat.
On the other hand, in the conventional planetary gear mechanism 200 of the tray shift mechanism, the center of an arc portion of the inner-tooth-rack 203 coincides with that of the sun gear 201, and engaged points between the respective gears are aligned on a straight line 1, as shown in FIG. 1. Thus, when it is assumed that r3 is a pitch circle radius of the sun gear 201, r4 is a pitch circle radius of the planet gear 202, and λ is a predetermined gap, it is difficult to design the sun gear 201 and the planet gear 202 such that the distance between the centers of the gears is set to be (r3+r4+λ) by adding the predetermined gap λ to the sum of the r3 and the r4 in order to prepare gears of desired modules or desired number of teeth having appropriate gap or spacing therebetween, as shown in FIG. 2.
In preparing gears of the planetary gear mechanism 200, it is the simplest way to make the distance between the centers of the sun gear 201 and the planet gear 202 equal to the sum of the pitch circle radiuses of the respective gears in view of designing of modules or number of teeth.
However, in reality, in case the predetermined gap λ is not secured, the problem of interference such as clog between respective gears which is caused by a slight change in condition or environment arises.
Furthermore, in the planetary gear mechanism 200, it is required that gears of sufficiently large modules be arranged in the limited space of the main body of the disc player.